Field of the Invention
Embodiments of the present invention relate to an image coding apparatus and an image coding method, more particularly to a technique for applying a filtering operation on a boundary of an image block.
Description of the Related Art
Recently, consumer use televisions capable of displaying a three-dimensional image (in other words, stereoscopic image or 3D image) have been prevailing. According to the principle of the three-dimensional image, an image for the left eye and an image for the right eye, which are created using the parallax between the left eye and the right eye, are projected into corresponding eyes individually to achieve a stereoscopic vision.
A variety of recording formats are available for the three-dimensional image and the side-by-side method is one of those formats. The side-by-side method is a three-dimensional image recording format in which an image for the left eye and an image for the right eye are subsampled by ½ each in the horizontal direction and the subsampled image for the left eye is arranged on the left side of a screen while the subsampled image for the right eye is arranged on the right side of the screen. The side-by-side method is adopted for satellite broadcasting and may be said to be one of the current mainstream recording formats for three-dimensional image. Japanese Patent Application Laid-Open No. 2010-068315 discusses a technique concerning the recording of three-dimensional image data based on the side-by-side method.
When a moving image is transmitted via a television broadcast wave or a moving image is recorded on an optical disk or a hard disk by a video camera or the like, usually, compressing and coding of the moving image is performed to reduce an information amount of the moving image. As one of typical moving image compressing and coding methods, H.264 (Moving Picture Experts Group 4 (MPEG4)-advanced video coding (AVC)) coding method is available. The H.264 coding method has been widely spreading so that it has been adopted as standards for advanced video coding high definition (AVCHD) which is a high definition recording method of video cameras, and One Seg broadcasting of terrestrial digital broadcasting. In future, the moving image compressing and coding technique is expected to be used when any three-dimensional image is captured by a video camera or the like and recorded in an optical disk or a hard disk. For example, the configuration of an apparatus may be considered in which a three-dimensional image by the side-by-side method is compressed and coded according to the H.264 coding method and recorded in a storage medium.
However, a following issue may occur when the three-dimensional image by the side-by-side method is compressed and coded using the H.264 coding method.
According to the side-by-side method, the image for the left eye and the image for the right eye are arranged in parallel and treated as a single image, so that a boundary between a right end of the image for the left eye and a left end of the image for the right eye exists in a central portion of a coding target image. According to the H.264 coding method, an inter-loop filter referred to as a deblocking filter is defined in its standard document and filtering is performed on the boundary between blocks in an image. The H.264 coding method is an effective processing for removing block noise if the image is a conventional two-dimensional image. In case of the side-by-side type image, right and left portions with respect to the boundary between the right end of the image for the left eye and the left end of the image for the right eye are separate images, so that the filtering deteriorates the quality of the images on the boundary.
Depending on cases, it may be preferable to omit the filtering processing on a specific region even if the procedure is defined in the standard document when an image generated by combining a plurality of different images is a coding target image.